1. Field of the invention
The present invention relates generally to lock and latch mechanisms and more particularly to latch mechanisms that are adjustable to accommodate differing door hardware backset dimensions.
2. Description of the Background
Entry doors on and in commercial and residential structures are commonly provided with a latching mechanism to a closed position when not locked, and/or a locking mechanism for securing them in the closed positions. In either case the retention and securing functions are accomplished by a bolt extending from the door and into the door frame to prevent movement. The bolt may be a spring actuated asymmetric latch bolt having a sloped face that is forced into the casing by contact with the strike plate to permit the door to latch closed on its own. Alternatively, a lockbolt with no sloped face may be manually extended or retracted. Such doors are equipped with hardware on their interior and exterior surfaces, typically a knob or lever rotatable on a spindle, to actuate the mechanism(s) and retract the bolt into the door and thereby allow the door to swing open. A number of different lock and latch mechanisms are available but the type known as tubular, or “bored through” locksets have become commonplace in residential and other applications. Tubular handlesets are designed to be installed in an industry standard pattern of holes drilled in an edge and face of the door. The distance from the latch edge of the door to the axis of rotation of the hardware spindle is referred to as the backset and dictates the position of the hole drilled through the face of the door. Two dimensions are standard in the industry: 2⅜ inches or 2¾ inches. To avoid the expense and complication of developing and offering separate lock and latch mechanisms for each backset dimension, it would be advantageous to provide a single mechanism capable of accommodating various backset dimensions.
Adjustable backset door latches have been developed which utilize various mechanisms to vary the distance between the door edge and the rotational axis of the latch knob, including slot and pin arrangements such as shown and described in U.S. Pat. Nos. 1,661,454 and 4,372,594, spring-loaded pins such as shown and described in U.S. Pat. Nos. 4,653,787 and 4,602,490, and push-and-twist arrangements such as U.S. Publication No. 20070290514. These devices require adjustment of multiple components when being adjusted from one backset to another. Specifically, when adjusting from one backset to another, all known adjustable backset door latches require at least two or three components to be moved to a new position. This takes significant effort and time. Moreover, once the adjustable backset door latch has been adjusted and installed in a door, it cannot be readjusted. Rather, it must be removed so that those two or three internal components can be moved to their new positions.
It would be advantageous to provide a mechanism that requires adjustment of a single component to adjust from one backset to another, can be adjusted in place even after initial installation on a door without complete removal, and which is simple to adjust and operate, efficient and inexpensive to manufacture, and durable and reliable for longtime use.